1. Field of the Invention
This invention relates generally to a system and method for optimizing the operation of a hybrid vehicle and, more particularly, to a system and method for predicting near future routes and driving conditions using a self-learning control and vehicle location to efficiently utilize the power sources of the hybrid vehicle.
2. Discussion of the Related Art
Hybrid vehicles are vehicles that use two or more distinct power sources to power the vehicle. Hybrid electric vehicles are most common, and typically combine an internal combustion engine with a DC battery and one or more electric motors or other mechanical system for driving the vehicle. Another type of hybrid electric vehicle is a vehicle that combines a fuel cell system with a DC battery and an electric motor or other mechanical system for driving the vehicle. An ultracapacitor and/or a flywheel may be used instead of, or in addition to, a DC battery in both of the previously mentioned hybrid vehicles, as any medium for storing electrical energy may be utilized.
Hybrid vehicles can operate using four different basic operating modes. A first operating mode includes driving with the electric motor or motors powered by the battery alone. In a second operating mode, the hybrid vehicle may operate by using the internal combustion engine or fuel cell system alone. In a third operating mode, a combination of driving with the electric motor or motors powered by the battery and internal combustion engine or fuel cell system. In a fourth operating mode, the hybrid vehicle is slowed down by utilizing regenerative braking, which enables charging of the DC battery or ultracapacitor.
Reduction of greenhouse gases is an important goal to address a variety of health and environmental concerns. Therefore, vehicle fuel efficiency is becoming more important, particularly with the inevitable tightening of corporate average fuel economy (CAFÉ) requirements. Furthermore, fuel prices are likely to climb as limited oil reserves are being depleted, particularly in light of the ever expanding world vehicle market. Thus, it is becoming more important to increase vehicle fuel economy whenever it can be cost effective to do so.
Hydrogen is an attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween. Some portion of fuel cell vehicles are likely to include a series hybrid arrangement, thus the scheduling of fuel cell power versus battery state-of-charge (SOC) is relevant to the efficiency and performance of the vehicle.
From just the fuel cell point of view, a hybrid vehicle is more efficient at lighter loads. From the vehicle point of view, a hybrid vehicle is more efficient while maintaining a fairly low state-of-charge of the battery or ultracapacitor because it can accept more regenerative braking energy. Unfortunately, if the battery is kept at a state-of-charge that is too low, it may hurt performance at times of high power demand, such as passing maneuvers or when ascending steep inclines. A low state-of-charge of the battery in a hybrid vehicle employing a fuel cell system may put the fuel cell stack in a high load condition for an extended period of time, which negatively affects the efficiency of the fuel cell system, and also puts difficult thermal demands on the system, such as requiring a large radiator area that may not package effectively in a vehicle, or force a larger, more costly and less efficient cooling fan.
Generally, if power demands of the hybrid vehicle are low, and if the vehicle is doing a lot of starts and stops, a low state-of-charge of the battery or ultracapacitor is the most efficient way to operate the vehicle because a low state-of-charge of the battery or ultracapacitor allows for the most regenerative braking energy. City-type driving is the best example of this condition.
Periods of high power demand are generally short-lived, such as when passing or ascending a steep incline, therefore, the most efficient way to operate a hybrid vehicle during high power demands is with a high initial state-of-charge of the battery or ultracapacitor. Since the battery or ultracapacitor can provide most of the power needed when it has a high state-of-charge, the fuel cell system is able to operate at a much lower, more efficient, load point and still provide the hybrid vehicle with the needed power.
Thus, to optimize hybrid vehicle efficiency, the battery or ultracapacitor state-of-charge needs to be low in city-type driving conditions, and high for high load situations, such as for passing or ascending steep inclines. However, appreciably changing the state-of-charge of a battery or ultracapacitor may take several minutes. Thus, it is impossible to raise the state-of-charge in a few seconds or less when it is suddenly needed. Therefore, there is a need in the art to be able to determine and/or predict future power demands of a hybrid vehicle to enable the state-of-charge of the battery or ultracapacitor to be prepared for high power demand events.